Coating removal from vane rings via tumble strip

Abstract

A method of removing a coating layer from a gas turbine component, including a step of applying both mechanical and chemical actions in a tumble stripping process to the coating layer of the gas turbine component, wherein the gas turbine component is bathed in an acid solution while being rubbed by a plurality of hard media elements in a tumbling motion.

1 . A method of removing a coating layer from a gas turbine airfoil component, comprising a step of applying both mechanical and chemical actions in a tumble stripping process to the coating layer of the gas turbine airfoil component, wherein the gas turbine airfoil component is bathed in an acid solution while being rubbed by a plurality of hard media elements in a tumbling motion. 
     
     
         2 . The method as defined in  claim 1  wherein the acid solution is adapted to dissolve aluminium but not substantially to dissolve nickel. 
     
     
         3 . The method as defined in  claim 2  wherein the acid solution comprises a dilute mixture of a nitric acid and ammonium bifluoride. 
     
     
         4 . The method as defined in  claim 2  wherein the acid solution comprises a nitric acid of 20-30% by volume mixed with ammonium bifluoride of 40-60 grams/litre. 
     
     
         5 . The method as defined in  claim 1  wherein the hard media elements are made of ceramics. 
     
     
         6 . The method as defined in  claim 1  wherein the hard media elements comprise porcelain stones. 
     
     
         7 . The method as defined in  claim 1  wherein the hard media elements are individually configured in a cylindrical shape. 
     
     
         8 . The method as defined in  claim 1  wherein the hard media elements are individually configured in a wedge-shape. 
     
     
         9 . The method as defined in  claim 1  wherein the hard media elements are individually dimensioned to provide a maximum surface measurement not larger than 0.375 inches on any side of the respective hard media elements. 
     
     
         10 . The method as defined in  claim 1  comprising a step of protecting a cavity of the gas turbine airfoil component which is not covered by the coating layer, from contact with the acid solution and the hard media elements during the tumble stripping process. 
     
     
         11 . The method as defined in  claim 10  wherein the protecting step is practised by applying a resin material to block the cavity prior to the tumble stripping process. 
     
     
         12 . The method as defined in  claim 11  wherein the protecting step is further practised by applying ultraviolet lights to the resin material to cure the same, prior to the tumble stripping process. 
     
     
         13 . The method as defined in  claim 12  wherein the protecting step is further practiced by heating the cured resin material until the same is burned out. 
     
     
         14 . The method as defined in  claim 13  wherein a grit blasting process is conducted to remove a dusk-like substance resulting from the burning process of the cured resin material. 
     
     
         15 . The method as defined in  claim 1  comprising a step of conducting a first grit blasting process to the gas turbine airfoil component prior to conducting the tumble stripping process. 
     
     
         16 . The method as defined in  claim 15  comprising a step of conducting a second grit blasting process to the gas turbine airfoil component after conducting the tumble stripping process. 
     
     
         17 . The method as defined in  claim 16  wherein the first grit blasting process is completed and the tumble stripping process begins when up to 30% of the coating layer material is removed. 
     
     
         18 . The method as defined in  claim 16  wherein the tumble stripping process is completed and the second grit blasting process begins when up to 90% of the coating layer material is removed. 
     
     
         19 . A method of removing a coating layer from a gas turbine component, the coating layer including at least one metal element different from a base metal of the component, the method comprising a step of applying both mechanical and chemical actions in a tumble stripping process to the coating layer of the component, wherein the gas turbine component is bathed in an acid solution while being rubbed by a plurality of hard media elements in a tumbling motion. 
     
     
         20 . The method as defined in  claim 19  wherein the acid solution is adapted to dissolve the at least one metal element in the coating layer but not substantially to dissolve the base metal of the component.